1. Circles in Contact
Lesson 2
J.Byrne 2015

2. Circles in Contact Externally
When circles are touching at one point on their circumference they are said to be in contact tangentially
The point of contact is called the POC.
The distance between the centres of the circles touching externally equals the sum of their radii
Solution : = 35 draw an arc of 35
J.Byrne 2015

3. Circles in Contact Externally
Question 1
Below are two circles Green circle has a radius of 30mm Red circle has a radius of 18mm
Draw a circle radius 30mm to touch both circles below. Show both POCs.
J.Byrne 2015

4. Circles in Contact Externally
Solution : = 60 draw an arc of 60
= 48 draw an arc of 48
Join centres of circles to show POC
Draw in new circle R=30
R = 60
R = 48
J.Byrne 2015

5. Circles in Contact Internally
In the circles below they are touching internally
The distance between the centres of the circles touching internally equals the difference between their radii
Solution : 60 – 20 = 40 draw an arc of 40mm from centre of big circle
R = 60
R = 20
J.Byrne 2015

6. Circles in Contact Internally
Question 2
Draw a circle radius 30 mm to touch both circles below. Show all POC’s.
R = 60
R = 20
J.Byrne 2015

7. Circles in Contact Internally
Solution 2
R20 + R30 = R Draw an arc of 50 from centre of circle small circle
R60 – R30 = R Draw an arc of 30 from centre of the big circle
R = 30
R = 50
J.Byrne 2015

8. Circles in Contact Internally
Join and extend all centres to show POC
Draw in new circle
POC
POC
POC
J.Byrne 2015

9. Circles in Contact Question 3 Draw the Wine glass shown below.
J.Byrne 2015

10. Wine Glass
Construct the lines you know first.
J.Byrne 2015

11. Wine Glass
J.Byrne 2015

12. Light Bulb
J.Byrne 2015

13. Draw this bottle
J.Byrne 2015

14. Draw in what you know for sure
J.Byrne 2015

15. Decide which circles are in contact and how
J.Byrne 2015

16. The bottle showing all the circles and arcs
J.Byrne 2015